The invention concerns an air-core choke coil, for use in high tension installations, and a method for its manufacturing. Air-core choke coils contain a helical winding, of a coil conductor, or several helical windings connected in parallel. The windings are formed into a helix by winding or bending the coil conductor, measures being employed to insulate sequential turns of a winding from one another.
Choke coils act to prevent rapid changes in the current magnitude and are also used for other various purposes. For example, they are useful as carrier frequency barriers, as short circuit choke coils for current limitation, as filter choke coils in resonant circuits, as current rise and smoothing choke coils, etc.
In a known air-core choke coil described in German Offenlegungsschrift 2,218,018, the coil has a winding in which the coil conductor is surrounded by insulating tapes and neighbouring windings are respectively bonded together. Such air-core choke coils are characterised by high mechanical strength and compactness but permit only axial air flow through the coil, which has an adverse affect on the cooling of the upper parts--particularly of the inner windings of multi-layer air-core choke coils. In addition, the magnetic field generated by the coil cannot escape from the coil conductor and cause eddy currents which further heat the coil.
Since the temperature of the coil conductor should remain below a certain limiting value, its cross-section must be enlarged to improve its efficiency cooling particularly when additional factors contribute further to heating it.